Boiler plant including two rotary regenerative air preheaters

ABSTRACT

In a boiler plant including two rotary regenerative air preheaters connected in parallel in conduits branched off from main air and gas ducts are provided flow distributing damper means controllable such as to keep the discharge temperatures of the gas flows from the preheater at the same value.

United States Patent Pettersson et al.

[54] BOILER PLANT INCLUDING TWO ROTARY REGENERATIVE AIR PREHEATERSinventors: Birger Pettersson, Alta; Bo Johnsson, Kungsbacka, both ofSweden Assignee: Swenska Rotor Maskiner Aktiebolag, Nacka, Sweden Filed:April 12, 1971 Appl. No.: 133,318

Foreign Application Priority Data April 14, 1970 Great Britain..l7,666/70 US. Cl ..165/7, 110/56, 122/DIG. 1,

122/1 A, 165/34, 165/101 Int. Cl ..F28d 19/00 Field of Search ..165/7,4, 10, 101, 34;

122/DlG. 1, 1 A; 110/56 References Cited UNITED STATES PATENTSRosencrants 1 10/56 [4 1 Sept. 19, 1972 1,779,276 10/1930 Jacobus........122/1)10. 1 2,320,911 6/1943 Cooper ..165/7 2,795,401 6/ 1957Cooper et a1. ..165/7 x 2,883,160 4/1959 P61611161 et a1. ..165/7FOREIGN PATENTS OR APPLICATIONS 717,782 11/1954 Great Britain ..110/56592,483 5/1925 France ..165/4 209,356 6/1960 Germany ..122/010. 1

Primary Examiner-Albert W. Davis, Jr. Attorney-Flynn & Frishauf [57]ABSTRACT In a boiler plant including two rotary regenerative airpreheaters connected in parallel in conduits branched off from main airand gas ducts are provided flow distributing damper means controllablesuch as to keep the discharge temperatures of the gas flows from thepreheater at the same value.

5 Claims, 1 Drawing Figure BOILER PLANT INCLUDING TWO ROTARYREGENERATIVE AIR PREI-IEATERS ducts.

Even though the two preheaters are of identical general constructionthey almost never have the same characteristics. For instance, they maypresent different resistances to flow and different tendencies toaccumulate soot and ash. Further, the flow patterns in the ducts andbranch conduits may also bedifferent. All these differences result indifferent heat transfer conditions so that the temperaturedrop of thegases is not the same in the two preheaters.

Of course it is desireable to utilize the heat contents of the gases tothe greatest possible extent. However, for certain reasons the gastemperature at the outlet from the preheater must not lie below apredetermined minimum value which may be different for different plants.On the other hand, the discharge temperature of the gas must not be muchhigher than this minimum temperature but lie at or closely above saidtemperature. It is evident that if the discharge temperatures of the gasflows from the two preheaters are different the heat contents of the gasflow of the higher temperature will not be sufficiently utilized.

Accordingto the invention there is provided an adjustable damper meansfor controlling the distribution of the main flow of one of the fluidsbetween the two preheaters. Such damper means makes it possible to keepthe discharge temperatures of the gas flows from the preheaters at thesame value under all operating conditions irrespective of differences inthe characteristics of the preheaters, flow patterns etc. The magnitudeof this value may be controlled in any suitable manner.

If the damper means is provided inthe air system the control of thetemperature level may be accomplished by by-passing a controllableportion of the total air flow. However, preferrably the damper means isprovided in the gas system while .each preheater is associated withmeans for by-passing at least part of the air flow passing through itsair branch conduit.

The invention will now be described more in detail with reference to theaccompanying drawing which diagrammatically illustrates an embodiment ofa preheater section of aboiler plant according to the invention.

The preheater section shown in the drawing includes two air preheatersof the well-known Ljungstrom type and of identical design eachcomprising a rotatable matrix and stationary air and .gas conduitconnections.

Flue gases from the boiler are supplied to the preheater section througha main supply duct 12 which divides into two branch conduits 14, one foreach preheater 10. After having passed through the preheaters 10 thegases are discharged through conduits 16 which merge into a maindischarge duct 18.

Air is supplied through two supply ducts 20, one for each preheater 10,and is discharged through discharge ducts 22. For each preheater thereis provided a bypass conduit 24 interconnecting the air supply anddischarge ducts and 22. At the branch point on each supply duct 20 isprovided a damper 26 by means of which the air quantity by-passedthrough the by-pass conduit24 can be controlled.

In the gas supply duct12 is provided a damper 28 by means of which thedistribution of the main. gas flow between the two preheaters can becontrolled. The

damper 28 is actuated by an adjusting device 30 governed bytemperaturesensing devices 32 located in the .gas discharge conduits 16.The signals from the sensing devices 32 bring the adjusting device 30 tomove the damper 28to a position in which the ratio gas flows from thedischarge conduits 16 can be re garded as thoroughly intermingled thereis located a further temperature sensing device 34 which controls anadjusting device 36 connected to the two dampers 26 bymeans of links 38.The adjusting device 36 is adapted to maintain the gas temperature inthe duct 18 at or closely above apredeterminedminimum value bythrottling the by-pass conduits 24 at increasing temperature in the duct18 andthereby increasing the air quantity passing through the preheatersand by increasing theby-passed air quantity when the temperature in theduct 18 tends to decrease.

From the foregoing description it is apparent that the gas damper 28serves to maintain the same temperature in both gas discharge conduitsl6 and that the air dampers 26 serve to maintainthe temperature in thegas discharge duct 18 at a predetermined constant value. However, onaccount of the inertia of the whole system certain temperatureoscillations are inevitable. If the temperatures in the two gasdischarge conduits l6 become differentthe .gas damper--28 is actuated tochange the relative magnitudes of the two gas flows accordingly. Suchtemperature oscillations need not necessarily affect the temperaturesensed by the sensing device 34 because the mean temperature may remainconstant. On the otherhand, if the temperature is the same in both gasdischarge conduits 16 but increases or decreases the air dampers 26 areactuated while the gas damper 28 is not actuated. Finally, if thetemperatures in the conduits 16 changes differently and in such a mannerthat the mean temperature also changes all dampers 26, 28 areactuated.

It is evident that the temperature sensing device 34 may be replaced bytemperature sensing devices in the gas discharge conduits 16 connectedto a simple computer device or the like'the outputsignal of the computerbeing indicative of the mean temperature.

The air maybe supplied to "the air ducts 20 by separate fans or theducts 20 @may form branches of a largerduct containing a single fan. Thefans may be of variable capacity. The airdischarge ducts 20 may lead todifferent parts of the boiler furnace or they may' merge into a singlelarger duct leading to the air distributing means of theboiler.

The temperature sensing devices and the adjusting devices may be ofconventional suitable types and the control system asa whole may bedesigned according to known principles.

What weclaimis:

l. Aboiler plant including two rotary regenerative air preheatersconnected in parallel in conduits branched off from a main air duct anda main gas duct, characterized by adjustable damper means positioned inthe main gas duct upstream of the preheaters for controlling thedistribution of gas flow between the two preheaters.

2. A boiler plant as defined in claim 1 in which temperature sensingmeans are provided in the gas outlet conduit of each preheater and thedamper means is adapted to be actuated by an adjusting device controlledby said temperature sensing means in such manner as to keep thetemperatures in the gas outlet conduits at the same value.

3. A boiler plant as defined in any of the preceding claims in whicheach preheater is associated with UNITED STATES PA'IENT OFFICEGE-R'EFIEFKCATE CORRECTION mm- :1 no. -3 692,096 Dated September 19,1972 u.n-v-L-=m.- er(e) BIRGER PETTERSSON BO aormssou It is certifiedthat: error appears in the above-identifiedpatent .zmd thug: saidLetters Patent are hereby'corrected as shownbelow':

Column 3 lines 13 arid 14', delete "any of the preceding c: lain 1s' andinsert elaim 1 Signed and sealed this 30th day or January 1973 (SEAL)Attesc: I

EDWARD M.FLETCHER,JR. ROBERT GOTTSGHALK Attes'ting Officer Commissionerof Patents.

1. A boiler plant including two rotary regenerative air preheatersconnected in parallel in conduits branched off from a main air duct anda main gas duct, characterized by adjustable damper means positioned inthe main gas duct upstream of the preheaters for controlling thedistribution of gas flow between the two preheaters.
 2. A boiler plantas defined in claim 1 in which temperature sensing means are provided inthe gas outlet conduit of each preheater and the damper means is adaptedto be actuated by an adjusting device controlled by said temperatUresensing means in such manner as to keep the temperatures in the gasoutlet conduits at the same value.
 3. A boiler plant as defined in anyof the preceding claims in which each preheater is associated with meansfor by-passing at least part of the air flow passing through the airbranch conduit.
 4. A boiler plant as defined in claim 3 in which theby-pass means include adjustable dampers interconnected in such manneras to change the rate of air flow through the preheaters to the samedegree in both preheaters.
 5. A boiler plant as defined in claim 4 inwhich an adjusting device for the dampers is controlled by meansresponsive to the mean temperature of the gas leaving the preheaterswhereby to keep said temperature at a desired level.